Answer:
Correct answer is They led to overcrowding, which resulted in disease.
Step-by-step explanation:
Last option is the correct one, as after Pericles ordered that all citizens of Athens should retreat to the city a great plague erupted. A lot of people died, including Pericles himself. Athenians were forced to surrender and destroy the city-walls.
All other options are thus wrong, because were not the main reason for the surrender.